In this paper, we discuss the role that teachers play in preventing the expression of blatant and subtle prejudice among students. Using a self-reported survey conducted in the south of France, we investigated the attitudes of 1,858 middle and high school students. Multivariate analyses show that when students see their teachers addressing issues about racism, discrimination and cultural diversity in the classroom, their attitudes of intolerance decrease. Nevertheless, mediation and moderation models highlight the existence of external factors, such as the parents' educational attainment, that affect the students' capacity to internalise their teachers' discourse. Contrary to our expectations, the students' level of trust in the education system has no significant influence on their perception of the effectiveness of teacher interventions.